So-called engineering plastics, such as polyacetal resin, ABS resin, polyamide resin, polyphenylene oxide resin, polyimide resin, thermoplastic polyester resin, polycarbonate resin, epoxy resin, thermosetting unsaturated polyester resin, phenolic resin and the like are extensively used in various industrial fields like the automotive industry and the electronic-electric industries on account of their high melting points or softening points as well as excellent mechanical properties.
Nevertheless, what are required for any resin used for parts having sliding surfaces like gears used in precision machines are a low coefficient of friction, that is, excellent sliding properties, and excellent friction/wear resistance, and in this respect, the aforementioned engineering plastics by themselves cannot be said to inherently possess sufficient sliding properties and friction/wear resistance.
Molded articles impregnated with grease or the like, as a sliding property improving agent, which have been used up to the present give rise to such problems that grease blooms or exudes to the surface with the result that neighboring parts are stained or the sliding properties improving effect does not last long enough.
There is available another method of incorporating a polymer like fluoroplastics or olefin plastics as an additive to improve the sliding properties of the aforementioned engineering plastics. Even though sliding properties of plastics are improved by this separate method, these polymer additives are accompanied by shortcomings associated with molding processibility such that peel-off of the polymer additive occurs in consequence of the phase separation on the surface of the molded article, due to their poor compatibility with said engineering plastics. Hence the mold release properties are inferior, on the top of the fact that fluoroplastics are generally expensive.